Thousands of Victorians who queued to take PCR tests over Christmas and the New Year will not receive their results because the samples are too old to be processed, as authorities scramble to improve virus figure accuracy.

The state posted 44,155 COVID-19 cases and four deaths on Sunday, with thousands of the new cases reported from tests taken up to four days ago.

COVID-19 Commander Jeroen Weimar said Melbourne Pathology had decided not to process samples from 7000 tests that were more than seven days old.

He said the health department agreed with the decision and apologised to those affected, who would have been awaiting their test results in isolation and had been notified by text.

"I think broadly we agree that there's a very low utility in results that are that old," Mr Weimar told reporters on Sunday.

"I would encourage anybody who is still symptomatic in that cohort - please come forward and get another PCR test.

"It is all part of that significant challenge we had over the Christmas and New Year's period, with the 300,000 or so traveller tests we had to process and all the other challenges over that period."

He urged those affected to take a rapid antigen test and monitor their symptoms.

Sunday's new infections included 22,051 from RATs and 22,104 from PCRs, the health department confirmed.

Mr Weimar said about 40 per cent of the RAT results were reported on Saturday, 4000 were from "a couple of days" prior and 2000 from four days ago.

He said PCR result delays were beginning to ease, with about half now coming back within 48 hours.

"That also means that half our results are taking longer than 48 hours, but we're working through our labs to get those times down and we're starting to see signs of improvement," he said.

"We are catching up, we haven't caught up yet."

About 30,000 RAT kits were handed out at PCR sites on Saturday, reducing wait times to under an hour, he said.

The state is now managing 146,863 active cases, with 752 patients in hospital, 108 more than the previous day, 104 in ICU and 23 on ventilators.

Meanwhile, Acting Premier Jacinta Allan announced Victoria will double the number of state-run vaccination sites available for children aged 5 to 11, with 36 sites around the state.

Most state clinics will begin vaccinating that age group from Monday, with support offered to kids suffering anxiety about vaccination or with developmental disabilities, autism or sensory needs.

Ms Allan said there were no plans to change the school return date for Victorian students.

She also confirmed the state's 2022 Australia Day parade had been cancelled due to community leader and stakeholder feedback, which called for the day to instead be marked through smaller events and activities.

The state opposition is calling for changes to isolation rules given high case numbers, including removing the requirement for fully vaccinated Victorians to isolate and take daily RATs if living with a positive case.

"We are putting forward a sensible suggestion about overhauling isolation requirements for emergency service workers, for healthcare workers and for those in critical supply chains, so that there is still food in our supermarkets so that our healthcare workers are not overstretched," opposition leader Matthew Guy said on Sunday.